1. Field of the Invention
The present invention relates generally to a magnetic card verifying device which is used as an electronic lock for entrance administration, membership system and the like. More particularly this invention relates to improvements thereof.
2. Description of the Prior Art
Various methods have been proposed for a magnetic card verifying device and the present inventor has previously proposed an influential method or system (disclosed in documents laid open to public inspection Nos. 40781/75 and 38738/76 of Japanese Utility Model Application examined). The above previously proposed system is summarized as follows. In the first, a magnetic card on which a reference magnetic signal (hereinafter referred to as a key code) having a large number of combinations was recorded is inserted into a verifying device in advance as a set card. And, when another magnetic card on which a magnetic signal or key code to be verified was recorded is inserted into the verifying device as a key card, the key codes respectively recorded on the set card and key card are compared and verified in the verifying device. Then, when both of the key codes are coincident with each other, the verifying device generates an output indicative thereof.
FIG. 1 is a schematic diagram showing an example of a magnetic sensor used in such verifying device. In FIG. 1, reference numeral 1 designates an I-shaped magnetic (saturable) core, 2 a primary winding which is wound around the magnetic core 1, 3 a secondary winding which is wound around the magnetic core 1 in the same way as in the primary winding 2, 4 a high frequency (approximately 500 kHz) oscillator connected to the primary winding 2 and 5 and 6 magnetic signal (key code) recorded sections (magnet or magnetized sections) of a set card and a key card, respectively. Reference letter V designates a voltage which is induced across the secondary winding 3. The saturable core 1 and the primary and secondary windings 2 and 3 constitute a saturable transformer S.
FIG. 2 is a graph showing an input to output characteristic of such saturable transformer type magnetic sensor as mentioned above. When a magnetic field H is applied to the saturable core 1 with the windings 2 and 3 by proper means instead of the key code recorded sections 5 and 6 and increased in its absolute value larger than the saturation magnetic field Hs of the core 1, the saturable magnetic core 1 is saturated as shown in FIG. 2. As a result, the output voltage V induced in the secondary winding 3 is rapidly decreased at the saturation points as shown in FIG. 2. Accordingly, in the case where the key code recorded section 6 is not loaded to the magnetic sensor, if the magnetic field A generated by the set card with the key code recorded section 5 is selected larger than the saturation magnetic field +Hs as shown in FIG. 2, the output voltage V from the magnetic sensor becomes small or substantially zero and the magnetic sensor is therefore turned off. Under this state, when the key card is inserted into the magnetic sensor or verifying device, the magnetic field or the key code recorded section 6 of the key card is applied to the saturable core 1. In this case, if the magnetic field generated by the key code recorded section 6 of the key card is oriented in the direction indicated by letter B which is opposite to the direction of the magnetic field A and is substantially the same in magnitude as shown in FIG. 2, the magnetic field B cancels the magnetic field A or the magnetic field applied to the core 1 becomes substantially zero whereby a predetermined output voltage V.sub.0 is induced in the secondary winding 3, thus the magnetic sensor being turned on to produce an output indicating that both the cards are coincident. While, if the magnetic field by the key code recorded section 6 is in the direction as indicated at B' in FIG. 2 or both the cards are not coincident, the magnetic fields A and B' are added together to be much larger than +Hs so that the magnetic sensor remains in its off-state and hence no output is delivered therefrom. Moreover, when the key card has no key code recorded section 6 (no magnet or is not magnetized), or both the cards are not coincident, namely, when the magnetic field by the section 6 is at point B.sup.0 in the graph of FIG. 2, only the magnetic field A is applied to the saturable core 1 so that the magnetic sensor is held also in the off-state and hence no output is delivered therefrom. Accordingly, when the output voltage V from the saturable transformer S indicates the result that the key codes recorded sections 5 and 6 or the set card and key card are compared and verified with each other. When a plurality of (for example, 6 to 8) magnetic signals or key codes are verified, a plurality of key code recorded sections and a plurality of saturable transformers corresponding to the former are utilized as the verifying elements.
FIG. 3 is a schematic diagram showing a constructional example in which a plurality of key codes are verified simultaneously according to the prior art system. In FIG. 3, like parts corresponding to those of FIG. 1 are marked with the same references where reference numeral 5' designates a set card and 6' a key card. In this case, reference numeral 5 designates not the magnet but a magnetic signal or key code recorded point which is magnetized on the set card 5' and reference numeral 6 designates a magnetic signal or key code recorded point which is magnetized on the key card 6'. Each of the saturable transformers S is the same as that in FIG. 1 and is shown more clearly from the electric point of view. The set card 5' with a plurality of key code recorded points 5 and the key card 6' with a plurality of key code recorded points 6 are located to grip therebetween a plurality of saturable transformers S such that the magnetic fields generated from the opposing key code recorded points 5 and 6 pass through the corresponding saturable transformer S. Reference numeral 7 designates an amplifier and 8 a verified output terminal. When each of the saturable transformers S is connected in chain or cascade as shown in FIG. 3, if any one of the saturable transformers S is turned off, the output is decreased as a whole and hence the whole of the saturable transformers S is made off. In other words, unless all of the saturable transformers S are turned on, the whole of the saturable transformers S is not turned on so that no output appears at the verified output terminal 8. Thus, the whole of a plurality of key code recorded points can be verified at the same time.
This prior art system described above has an advantage that the key codes recorded on the magnetic card as many dots can be compared and verified with one other by a simple circuit construction and a few of electronic parts thereof and a stable DC output is generated only when the key code signals recorded on the key card 6' are coincident with those on the set card 5'. However, this prior art system is not free from the possiblity that when a large current is flowed near the verifying device by construction work or intentionally, or in the case of lightning, without inserting the key card into the vefifying device, the saturable transformer S thereof is instantly made on by electromagnet or electrostatic induction voltage caused thereby and hence an output is generated therefrom. The first reason therefor is: since the output voltage from the saturable transformers S connected in cascade as shown in FIG. 3 is small as approximately from 0.2 to 0.3 Vpp and this output voltage is amplified and rectified to provide the verifiedcoincident output, the verifying device is apt to be disturbed; and the second reason is that since the saturable transformer S in each magnetic sensor of the verifying device is arranged in such a manner that it is turned off normally or in verified-incoincident state, while it is turned on when the verified result is coincident. As a result, when the saturable transformer S is turned off, the disturbing voltage is applied to the small output voltage generated from the saturable transformer S, the output voltage becomes large and the saturable transformer S is turned on. In practice, it is quite rare that the verifying device is disturbed to malfunction. However, in the verifying device utilized for the door-locking system, even such a small possibility of disturbance or the like is not negligible. Therefore, it is necessary to prevent the verifying device from being disturbed to malfunction.